Asphalt shingles and roll roofing have been produced in the same general manner for many years. The industry initially used an organic fibrous mat or an asbestos fiber mat as the preformed carrier. Mats of this type contributed significantly to the strength and flexibility of the finished product. Normally they were saturated with unfilled asphalt for waterproofing purposes, then coated with a thickness of filled asphalt in which a layer of roofing granules subsequently was embedded. The asphalt layer acted as a further waterproofing layer and held the granules in place. The granules and the fillers in the asphalt layer also protected the asphalt against the deleterious action of ultraviolet rays.
Later, the industry began moving more to the use of fiberglass mats instead of the conventional organic fibrous mats or asbestos fiber mats. Because fiberglass mats are much more porous than the previously used mats, this change eliminated the need for asphalt saturant. Instead, filled asphalt previously used only for the coating layer was now used both to impregnate and to coat the mat. Thus the properties of the filled asphalt became more critical. In addition to its waterproofing and weather resistant characteristics, the filled asphalt had to contribute more to the strength of the product, providing stability against deformation at roof temperatures and withstanding stresses encountered in the manufacturing process. Also, it had to adequately resist stresses due to handling by workmen and encountered by enviromental conditions such as wind loading and thermal stresses.
The filler which has been used by the industry is mineral in nature comprised, for example, of ground limestone, silica, slate, trap rock fines, and the like, and is present in the asphalt in substantial amounts. Typically, the filler used in these conventional roofing products has a specific gravity of between about 2.5 and about 3, which is several times more dense than the asphalt which it extends or displaces (the specific gravity of asphalt is about 1.0). Thus a filler content of about 60% by weight yields a filled asphalt having a specific gravity of about 1.7.
As the fibrous mat amounts to a very minor percentage of the total weight of the complete roofing element, a substantial portion, about 55%, excluding the weight of any roofing granule coverage, is comprised of this mineral filler.
The demand for fiber glass based asphalt roofing products has increased greatly since they were first introduced, to the point where they are now the standard product in the industry. During that time, however, their physical characteristics have remained substantially the same while their cost has risen with the rise in costs of their component elements. While it would of course be desirable to produce roofing products of at least as high quality at a lower cost, it is apparent that this goal has not been attained to any significant degree. The length of time that has passed since the introduction of fiber glass based asphalt roofing products is indicative that the problems which must be overcome in order to achieve this goal are considerable.
In looking for a way to improve the product through redesign, the base mat is not a likely element to change since the fiber glass mats conventionally used are quite low in weight already and are not likely to be replaced by a less expensive material without sacrificing desirable properties. As to the coating layer, the filled asphalt cannot be reduced in amount without sacrificing aesthetic properties or running the risk of poorer performance. A relatively thick layer of filled asphalt is desired in roofing shingles in order to provide a thick butt portion, which is considered aesthetically pleasing due to the shadow line it creates on the roof. Further, if the layer is too thin the roofing granules will not be held in place as securely as in a thicker layer.
Because asphalt is more expensive than the conventional filler material, the use of less asphalt overall, without reducing the amount of filler, has been tried by others. The result has been a cheaper roofing product, but one which cannot weather to the same level as a product with more of the same quality asphalt. Further, a significant reduction in asphalt can create processing problems. The more the amount of asphalt in a given mix is reduced, the higher the concentration of filler in the mix. This increases the viscosity of the mix and could cause flow problems through the processing equipment. One way to combat this is to heat the asphalt or the filler or both, since the addition of heat will lower the viscosity. The addition of heat over and above the standard processing temperatures, however, would move the temperature of the asphalt closer to its flashpoint.
The filler itself cannot be reduced to any economically significant extent because of the part it plays in all the various relationships with the asphalt. For example, it must be present in amounts sufficient to provide stability against deformation at high roof temperatures and to decrease degradation from ultraviolet rays.
Against this background it did not appear possible to redesign asphalt roofing products so as to retain all the beneficial performance characteristics of the standard design while at the same time significantly reducing costs. Surprisingly, the present invention achieves this result in a manner which not only satisfies the goal of cost reduction without sacrificing quality, but also provides a number of other benefits.